Apparatus for coating conduit sections



Sept. 29, 1959 G. L. HEATON ETAL 2,906,238

I APPARATUS FOR COATING CONDUIT SECTIONS Filed March 25, 1955 6 Sheets-Sheet 1 GEORGE LHE'ATON 8 ARTHUR H. VAUGHAN,

IN V EN TORS.

HUE'8NER,BEE'HLER, WORREL 1 HEPZ/G,

ATTORNEYS.

G. L, HEATON ETAL APPARATUS FOR COATING CONDUIT SECTIONS Filed March 25, 1955 Sept. 29, 1959 2,906,238

e Sheets-Sheet 2 GEORGE LHEATON 8 ARTHUR h. VAUGHAN 1N VEN TORS- HUE'BNER, BEE/ll. ER, WORRE' L 8 HERZ/G, By A TTORNEVS.

Sept. 29, 1959 a. L. HEATON ETAL 2,906,238

APPARATUS FOR COATING CONDUIT SECTIONS Filed March 25, 1955 6 Sheets-Sheet 4 050005 LJHEATON a ARTHUR H. VAUGHAN,

IN V EN TORS.

HUEBNER, BEEHLER,

Sgpt. 29, 1959 G. L. HEATON ETAL 2,906,238

APPARATUS FOR COATING CONDUIT SECTIONS Filed March 25, 1955 6 Sheets-Sheet 5 GEORGELHEATON 8 ARTHUR H. VAUGHAN,

INVENTORS.

HUEBNER, BEEF/L679,

WORREL 8 HERZ/G ,4 7' TORNEKSZ Sept. 29, 1959 G. L. HEATON ET L APPARATUS FOR COATING CONDUIT SECTIONS Filed March 25, 1955 6 Sheets-Sheet 6 GEORGEL-HE'ATON 8 ARTHUR H. l AUGIMN,v

INVENTORS- HUEBNER,BEEHLER, WORREL 8 HERZ/G,

ATTORNEYS.

APPARATUS FOR COATING CONDUIT SECTIONS George L. Heaton, Palos Verdes, Calif., and Arthur H.

Vaughan, Salem, Ohio, assignors to Rome Cable Corporation, Torrance, Calif. a corporation of New York Application March 25, 1955, Serial No. 496,836 Claims. Cl. 118-66) The present invention relates to coating conduit sections with molten material, both inside and out, particularly to coating metal conduit with a protective metal coating, and more particularly to galvanizing steel conduit sections both inside and out.

Reference is here made to US. Patent No. 2,110,893, issued to T. Sendzimer on March 15, 1938, for a Process for Coating Metallic Objects With Layers of Other Metals.

The continuous and efiicient coating of the internal and external surfaces of conduit sections poses difiicult engineering problems. This is especially true in the case of coating metal conduit with metal coatings. In the internal and external galvanizing of rigid steel conduit, for ex- 1 ample, for the protection of electrical systems, it is necessary to continuously pass conduit sections through a series of operations. To do this eifectively on a mass production basis, carefully designed automatic machinery and control means are required.

Furthermore, the coating on the conduit sections must, among other things, be uniformly and strongly adherent and must Withstand treatment such as bending as well as to resist corrosion. In the case of electrical conduit, the coating should be smooth to offer low friction for easy pulling and the finished conduit should have uniformly good bending qualities.

Accordingly, an important object of the present invention is to provide an apparatus for coating conduit, both inside andout, with a continuous,.uniform coating of molten material.

Another object is to continuously coat metal conduit sections, both inside and out, with a strongly adherent, uniform coating of protective metal.

An additional object is to continuously and efficiently coat ferrous metal conduit sections with a uniform, strongly adherent protective coating of zinc or zinc alloy.

These and other objects will be apparent upon reading the following description.

Broadly stated the present invention comprises the provision of an apparatus for continuously moving conduit sections through a series of operations, including cleaning and preparing the internal and external surfaces of the sections, such as by oxidizing and burning organic matter therefrom, forming a bonding surface on the cleaned sections, such as by reducing the oxide surface to a clean metallic surface, dipping the reduced conduitsections in a bath of molten coating material to coat the internal and external surfaces thereof, and removing or wiping the excess of coating material from the internal and external surfaces of the conduit sections. The apparatus employed comprises, in series arrangement, an oxidizing furnace, a reducing furnace, a molten coating material tank or pot and a wiping apparatus together with an interconnecting synchronized conveyer system and power drive means for continuously and automatically moving conduit sections through the furnaces, dip tank, and wiping apparatus under controlled operating conditions.

V A more detailed description of a specific embodiment of the apparatus of the invention as applied to galvanizing steel conduit sections is given with reference to the draw ings, wherein:

Figure l is a diagrammatic plan view showing the apparatus in series flow arrangement;

Figure 2 is a partial vertical cross-sectional view taken on the line 22 of the oxidizing furnace shown in Figure 1;

Figure 3 is a partial cross-sectional plan view of the oxidizing furnace and auxiliary equipment shown in Fig ure 2;

Figulre 4 is an elevational view of the oxidizing furnace shown in Figure 3 taken along the line 44; Figure 5 is a detail cross-sectional view taken onthe line 55 of Figure 3 and showing a screw conveyer and a portion of a conduit section;

Figure 6 is a vertical cross-sectional view taken on the line 66 of Figure 1 and showing the reducing furnace and auxiliary equipment;

Figure 7 is a cross-sectional plan view of the oxidizing furnace taken on the line 77 of Figure 6;

Figure 8 is an elevational view taken along the line 88 of Figure 7 and showing the operation of a conduit section transfer arm;

Figure 9 is a partial detail view taken along the line 9-9 of Figure 10 and showing a screw conveyer, tube hold-down and guide mechanism and associated gas injection equipment;

Figure 10 is a vertical cross-sectional view of the re ducing furnace and auxiliary equipment taken on the line 101tl of Figure 6;

Figure 11 is a partial, broken elevational view taken along the line 1111' of Figure 10 and showing a screw conveyer associated with transfer rollers at'each end thereof;

Figure 12 is a vertical sectional view taken on the line 12l2 of Figure 1 and showing a star wheel conveyer together with associated guide and transfer mechanism positioned in a zinc pot;

Figure 13 is a'similar view taken on the line 1 3- 13 of Figure 12 and showing a magnetic roller conveyer for withdrawing galvanized conduit sections from the zinc P Figure 14 also is a similar view taken on the line 1414 of Figure 13 and showing the star wheel conveyer associated with the guide and transfer mechanism in the zinc p FigurelS is a partial perspective view showing the star wheel conveyer and associated control mechanism;

Figure 16 is an elevationalview showing a zinc pump mounted above the zinc pot adjacent the star wheel conveyer;

Figure 17 is an end view of a star wheel bearing; and

Figure 18 is a cross-sectional View of the star wheel bearing of Figure 17 taken along the line 18-18.

Steel conduit sections it are obtained from a pipe or tube mill in predetermined length and diameter and contain more or less grease and oil both internally and externally. These conduit sections are spread out in parallel arrangement on the skids of loading rack 11-, and each section in turn is engaged simultaneously at two points in end threads of parallel screw conveyers 12 and 13. Screw conveyer 12 is provided with a right-hand thread and is driven in a counterclockwise direction and screw conveyer 13 is provided with a left-hand thread and is The chamber of furnace 14 preferably is maintained Patented Sept. 29, 1959 at a.temperature just below about 900 F. and especially at about 700 to 1000 F., by means of flame heaters 17. The heaters 17 are positioned on the furnace so that conduit sections at 16 are uniformly heated and carbonaceous matter is burned from boththeinternal and external surfaces thereof and a thin, uniform coating of iron oxide is formed over the entire surface of the sections both internally and externally. The iron oxide coating produced is not a definite scale, but is a tightly adherent coating. Types of heaters other than flame heaters can be used for this purpose.

To facilitate the cleaning and oxidizing of internal surfaces of the conduit sections, air is injected inside the individual sections by means of an air injection pipe 18. The pipe 18 is provided with a series of slots, such as slots 20 shown on Figure 9, along the inner wall thereof adjacent the ends of the conduit sections so that jets of air are continually injected into and through the interiors, of the conduit sections. A second compressed air conduit 19, similar to that shown at 18, is placed at the other end of the oxidizing furnace 14' and the slots therein are arranged so that the jets of air issuing therefrom do not oppose the jets from slots in pipe 18. In this manner, air is assured passage through the heated conduit sections without interference from opposite sides of the sections. As the cleaned and oxidizedconduit sections approach the far side of oxidizing furnace 14, they are forced off the ends of screw conveyers 12 and 13 and onto transfer conveyer rollers 21. Retarding risers, such as risers 45, shown in Figure 11, are provided to effect a uniform time sequence between tubes.

The rollers 21 continuously transfer the oxidized conduit sections from oxidizing furnace 14, through a small opening 22 in the end wall of the furnace and through a similar opening 23 (Fig. 7) in the end wall of adjoining reducing furnace 24. A similar set of rollers 26, con-. tinuously moves the conduit sections into the end portion of reducing furnace 24 until they contact a stop 27. Rollers 21 and 26 are tied in with the main drive-motor 25 to give constant timing at all speeds between the oxidizing furnace 14 and the reducing, furnace 24. The contacting of stop 27 by a conduit section sets in motion a transfer mechanism (not shown) which transfers the conduit section from rollers 26 to the ends of parallel screw conveyers 28 and 29.

The transfer from rollers 26 to the ends of screw conveyers 28 and 29 is accomplished by means of a series of retarding arms 31 (Figure 8) fixed to a rotatably mounted shaft 32. These arms assure a uniform time sequence between conduit sections and prevent crossthreading on the screws of the conveyers. The extremities of arms 31 are provided with hooks 33 which, upon rotation of shaft 32, engage a conduit section, such as 34, and as shown in phantom in Figure 8, urge the conduit section 34 from rollers 26 and transfer them to inclined edges 36 beyond shoulders 37. The conduit section 34 rolls against the ends of the screws of the conveyers 28 and 29 and is engaged by the end convolutions of the screws which preferably are made of somewhat greater diameter than the succeeding convolutions to provide a stop' for the sections as they roll against the ends of the screws and to prevent cross threading. Also, the distances between the end convolution and the succeeding convolution in each screw preferably are made somewhat greater than the pitch to avoid cross threading in the screws and to facilitate the engagement of the conduit sections 34 without causing jam-ups in the furnaces.

The worm of conveyer 28 is provided with a rightehand thread and that of conveyer 29 isprovided with a lefthand thread and the former is rotated in a counterclockwise direction while the latter is rotated in a clockwise direction to convey conduit sections 34, at a uniform synchronized rate, through the reducing furnace 24. This rate is synchronized and connected, in proper. phase relationshipwith the rate of transfer of conduit sections through oxidizing furnace 14 by means of a variable coupling 15 or similar suitable arrangement between furnaces 14 and 24. A reverse gear also is included with variable coupling 15 for the purpose of emptying reducing furnace 24 in the event of operation difiiculties.

Reducing furnace 24 is maintained at a temperature above about 1300% F. so that the conduit sections will be annealed to produce a: uniformly soft and ductile, easily bendable conduit while the oxide coating thereof. is reduced. The operating temperature of the reducing furnace preferably. i'smaintained'in the range of. about 1350 F; to about 1400 F. by means of regenerating heaters 33; fired. by means of: gas combustion, for. example. Other means of heating reducing furnace 24 can, of course. be employed. A hydrogen'atrnosphere is maintained in the reducing furnace 24 at a pressure slightly above atmospheric. The hydrogen for this purpose is produced by catalytic dissociation of ammonia and-contains 25 percent by volume of. nitrogen. Hydrogen can. be prepared by any other desired method, but should be relatively free of. components that react with iron. or oxides of iron at elevated temperatures.

As, the. oxidized conduit sectionsv are conveyedthrough reducing furnace 24, the oxidized coating on both the inside and outside surfaces ofthe conduits is reduced to a relatively pure, tightly adherent metal coating. This. metall coatingis relatively free of such undesirable impurities as carbon, sulphur, phosphorous and dissolved gases. To insure a freshly reduced coating of iron both inside and outside the conduit sections, a pipe 39'provided with a series. of slits- 20' along. the; inside. length' thereof is positioned alongthesidewall of'the reduction furnace 24. Hydrogen gas is forced into the pipe 39 by means of a blower-40and isyinjected into-the ends-of: the.conduit sections moving on the screw conveyers 28 and 29' through the slits 20. A similar pipe 39 is positioned along, the: otherside of 'reducing furnace. 24and jets of hydrogen gas, staggered with relation to. thefirst set:of; jets, similarly are injected into. the. ends of conduit'sections, as they pass through the reduction furnace.

Conduit sections hold-down members- 41' are placed.

along both sidesof thereducing'furnace 24.and.are sup ported by arms 42 (Fig. 10) pivotally mounted at. 43, the members 41 being disposed above the conduit sections near both: ends thereof to hold'the conduit sections.

in positionrinthe. screw conveyors-28 and 29: in parallel relationship to each other, as they move through the reducingfurnace 24.1 The=screw conveyors 28 and 29 are rotated in opposite. directions, thereby conveying the conduit sections while thereverserotation tends toiprevent longitudinal movementof'the conduit sections, in a lateral'direction relativeto the conveyors, thereby. preventing the ends of. theconduit sectionsfromv dragging against the brick walls of the furnace and bending or jamming. The arms 42 may be rotated about their pivot points 43 to swing the hold-down means 41' from an operative position in contact with the conduit sections near the endportions thereof toaninoperative position clear of the conduit sections by. manual rotation of the cranks 43' extending outwardly of the furnace 24.

A portion of the reducing furnace 24, atthe far end thereof, is partitioned off by means of partition 44. This portion of the furnace is maintained at a lower temperature than the reducing and annealing portion to cool the reduced and annealed conduit sections to a temperature approaching about l000 F. so that they will gradually approach the temperatureof the molten zinc bath( about 830 F.), before being dropped therein, to avoid shocking.

This is accomplished; by passing-cooling gases, at proper cooling temperatures, through the regenerating units 46, in this portion of the furnace, instead of using them as heating means.

As each partially cooled, reduced conduit. section washes t e end of conveyers 28 and 29, it is forced' cooling section of reducing furnace 24 through an open ing 49 in the wall thereof and deliver the conduit sections to a similar set of transfer conveyer rollers 51, located at the entrance side of a zinc pot 52 (Figure 12).

After each of the conduit sections on rollers 51 strikes a stop (not shown), retarding transfer arms 53, similar to retarding arms 31, are actuated and lift the conduit sections over the edges of rollers 51. In doing so, the conduit section is placed across the ends of runners 54 and 56 and is permitted to roll toward the surface 57 of the molten zinc in zinc pot 52. The conduit section in thus rolling comes into contact with the trailing edges of the spokes on star wheels 58 and 59.

The spokes of star wheel 58 are advanced 7' with respect to those of star wheel 59, so that the end of a conduit section contacting the spokes of the former star wheel is introduced below the surface 57 of the molten zinc in advance of the end of the conduit in contact with the spokes of star wheel 59. The latter end is the last to be submerged below the surface 57 of the zinc and, in being conveyed through the body of molten zinc in tank 52, is maintained at a higher level in the zinc bath than is the end first to be submerged, until passing the lowest point of travel, when the inclination is reversed.

During the passage of each of the conduit sections through the body of molten zinc, the peripheral edge of the star wheel serves as a hold down means to keep the conduit section submerged in the molten zinc. The runners 54 and 56 serve as guides defining the lower limit of the path along which the submerged conduit section moves through the body of molten zinc until it passes the arcuate portions of the runners.

At the far ends of the runners 54 and 56 are curved runner portions which guide the submerged, galvanized conduit sections from beneath the star wheels 58 vand 59 toward the exit side of the zinc pot 52. The lower end of the submerged conduit section is held down by a holddown member 1, whereas the higher end of the conduit section is passed over the far end of the runner 56 and elevated by an actuated lift-arm 62, while the lower end of the conduit section is moved along between the far end of runner 54 and hold-down member 61 by a transfer arm. 63. Arms 62 and 63 are actuated by power, means indicated at 64 and connected to the arms by power.

transmission means 66.

To avoid the entrance of ash floating on the surface 57 of the molten zinc'into the interiors of the conduit.

section and forming an occlusion in the internal galvanized coating, it has been found desirable to inst-all .a

zinc pump 67 (Figure 16) adjacent the point at which the highermost end of the conduit section enters the molten zinc bath, In the zinc pump a motor 68 drives a propeller 69 submerged below the surface of the zinc' bath and introduced into the end of a section of bent pipe 71. The action of a propeller drives liquid zinc through the pipe 71 and into the surface layer of the zinc bath at the point at which the highermost end of the conduit section enters the bath. This action clears an area of the zinc bath surface 57, free of floating ash at the region in which the end of the conduit section en ters the bath. It has been found that in this manner occlusion of ash in the internal wall of the conduit section is substantially completely avoided.

A special type of bearing has been developed for the star wheels to avoid difliculty with the molten zinc. crusting on the bearing from time to time. This bearing, as shown 'in Figures 17 and 18, is composed of anupper half section 72 and a lower half section 73 held together by means of screws 74. 'A carbon bearing insert 76'is placed in the shaft support portion of the lower half 73 Of the bearing assembly. The shaft 77 of the star wheel turns in the carbon insert 76. -When:it is desired to make changes in the bearing, or do maintenance work device 79 adapted to avoid damage due to overloads,

such as caused by jamming of the star wheels by jammed conduit sections, on the shaft by shutting off the power to the star wheels when an overload develops. This is accomplished by means of a cut-off switch 81 attached to the overload bearing 79. A friction brake 82 also is attached to the shaft 77 of the star wheels for fixing the star wheel in a given position when it is desired to do so during repair or maintenance operations, for example. A lift-arm control mechanism is shown at 83 for controlling the lift-arms 62 and 63 by means of switches 84 and 86 actuated by cams 87 and 88, respectively.

The galvanized conduit sections are then withdrawn from Zinc pot 52 by any convenient means, preferably by means of a magnetic roller conveyer as described in detail in co-pending application, Serial No. 494,853 to Otto Bernhardt, and filed March 17, 1955. The excessv of zinc is then wiped from the external and internal surfaces of the galvanized conduit section by any suitable means, preferably by means of an air and steam wiping method and apparatus 89 (Figure l) as described in detail in the above mentioned co-pending application.

The hot galvanized conduit sections, wiped free of excess zinc .both internally and externally are engaged by the chains 91 of a conveyer and rolled on runners 92 to straighten bowed conduit sections; The speed of chains 91 is controlled by a variable speed drive 93 which is set to control the degree of cooling of the galvanized conduit sections to permit spangles of zinc to form in the coating, rather than a coarse crystalline zinc structure, before quenching in the chromate bath 94.

The speed of the pintle chain conveyer 96 is controlled by variable speed control 97 to control the formation of a zinc chromate conversion coating on the galvanized conduit sections being conveyed through chromate bath 94. If the passage through bath 94 is too slow, a damp chromate coating results which etches the zinc coating. After passage through bath 94, conveyer 96 transfers the chromate conduit sections onto an inspection and unreversing the direction of rotation of the rolls 48. This is done by means of reversing gears 102. The thus withdrawn conduit sections are dropped into a water tank indicated at 103 (Figure l).

The cooled conduit sections are then transferred ,to a bath indicated at 104 containing a corrosion inhibitor, such as a soluble oil, to protect the freshly prepared surface of iron on the inside and outside of the conduit section. The thus protected conduit section is then coated internally and externally with the desired enamel by any suitable method, such as by dippingand then wiping the excess enamel from both the inside and outside surfaces of the conduit.

Water tank 103 also serves as a receiver for reduced conduit sections in cases of emergency, such as when a stoppage develops beyond the furnace 24 in the zinc pot or wiping mechanism and it is not desired to shut down the operation of the oxidizing and reducing furnaces while the stoppage is being corrected.

It will be noted that the use. of transfenrollers 21 and 26' and 48? an'di51'permits' the use" of only small openings 23, 49fand101 through the walls of reducing furnace 24. This results inlow hydrogen consumption. As indicated at 106 (Figure 1), hydrogen escaping through opening 23 is burned as a pilotfiame for reasons of'safety.

In the. specific embodiment described above, the apparatus oftheinventionhas been applied to coating from or: steel pipe with. zinc. It will be understood; however, that. the invention can be applied to placing multiple coatings of zinc or other metals or coatings on iron or steel pipe or conduit'or conduit made ofother metals. In addition, the invention can be used to apply'coatings of'various types; both metallic and'non-metallic, to various. types of'conduit sections, both metallic and non-metallic.

Furthermore, although certain structures and design features, including structure and design of certain auxiliary equipment and drive means, have been shown in describing the specific embodiment of the invention, it will be understood that such features can" be varied and modified considerably as to details and structure, as will occur to one skilled in the art. Accordingly,- although a' specificembodiment oftheinvention has been described above, it will be understood that such changes and modifi'cations in the apparatus of the invention can be made within the scope of the appended claims'without'departing-fromthe spirit of the invention;

What is cl'aimed'is:

1. Apparatus for coating tubular metallic bodies, including first and second furnaces, means providing a molten bath of coating metal, means for moving the bodies through said furnaces insequence, means'for delivering heat and an oxidizing gas atmosphere into the firstf'urnaceand heat and-a'reducing gas atmosphere into the second furnace'to-surround the metallic bodies-therein, means in saidreducing furnace for jetting a portion of the gasatmosphere in said furnace through the interior of the bodies asthey' move-through the'furnace, means for transferring the bodies ftom within-the re-- ducing'furnace to the molten'bath'and submerging them therein, to-coat the interior and exterior surfaces thereof while protecting them from contact with oxidizing gas,

means for moving the bodies through and'removing them fromthe bath, and means for removing excess coating from the surfaces of'the-bodies.

2 Apparatus for coating tubular metallic bodies, in-

cluding a reducing furnace, means providing a molten bath of coating metal, means for movingoxidized bodies throughthe reducing furnace, means for delivering areducing gas atmosphere into the reducing furnace tosurround the metallic bodies-therein, means-in said reducing furnace for jetting a portion of the gas atmosphere in said furnace through the interior of the'bodies as-they move through said reducing furnace, meansfor transferring the bodies from within the reducing furnace to the molten bath and submerging them therein vto-coat the interior and exterior surfaces thereof while protecting themfrom contact with oxidizing gas, means for moving the bodies through and removing them from the bath, and means for removing excess coating from the surfaces of the bodies.

3; I11 apparatusfor the treatment of tubular metallic bodies-priortodipping in a coating bath, a furnaceincluding means for: delivering into said furnace, to surround the bodies therein, a: reducing atmosphere reactivewith the bodies, meansfor heating 'the bodies and the atmosphere to a reactive temperature, means for moving the bodies through the furnace in aligned and parallel relation in a direction at right angles to: the

length'of'the bodies, and jet means inthe furnace arranged to deliver a portion of the reactive atmosphere f'romthe furnace into anend of the bodies as they move pastthejet means,

42 In apparatus" for the treatment of tubular bodies prior to dipping inacoating bath, a furnace including'means' for delivering into said furnace, to surround? the bodies therein, a reducing atmosphere reactive with the bodies, means for heating the bodies and the at mosphere to a reactive temperature, means for moving the bodies through the furnace in aligned and parallel relation in a, direction at right angles to the length of the bodies, and a plurality of jet means in the furnace adjacent each longitudinal edge of'the space traversed by the bodies to deliver a portionof'the reactive atmosphere from the furnace into the' ends of'the bodies as they move through the reducing furnace along a fixedpath and in aligned and parallel'relation in a direction'at right angles to the length of the bodies, means for delivering a reducing atmosphere into said furnace to surround the tubular bodies therein, fan and ductmeans in the-reducing furnace; said duct means extending alongside said path and-having jet apertures therein whereby a portion of the reducing atmosphere from thefurnace may be recirculated and'delivered in streamsthrough the interiors of 'the tubular bodies therein;

6. In apparatus for the treatment of tubular metallic bodies prior to dipping ina coating bath, an oxidizing furnace having means for delivering into the furnace'a heating and oxidizing atmosphere to surround the surfaces of the tubular bodies therein, a reducingfurnace positioned laterally of one end of theoxidizing furnace and provided with means for delivering into the reducing furnace a reducing atmosphere tosurround the bodiestherein for continuously reducing the oxide coating ofthe tubular bodies to metal, means for continuously moving said tubular bodies broad-side in parallel'orientation for continuously removing the tubular bodies longitudinally one at a time from the other end of the reducing furnace, means in the oxidizing furnace for blowing air longitudinally through the tubular bodies, and'means in the reducing furnace for blowing a portion of the reduc--- ing atmosphere from saidreducing furnace longitudinally through the tubular bodies therein.

7. In apparatus for the treatment of tubular metallic bodies prior to dipping in a coating bath, an-oxidizing furnace having means for delivering into the furnace aheating and' oxidizing atmosphere to surround'the surfaces of the tubular bodies therein, a reducing furnace positioned laterally of' one end of the oxidizing furnace and provided" with means for delivering into the reducing furnace a reducing atmosphere to surround the bodies therein for continuously'reducing the oxide coating of the tubular bodies to metal, means for continuously moving said tubular bodies broad-side in parallel orientation through'the oxidizing furnace, means for continuously transferring-said tubular bodies longitudinally one at a time from said one end of 'the oxidizing furnace to the adjacent end of the reducing furnace, means for continuously moving said tubular bodies broad-side in parallel orientation through the adjacent end of the reducing furnace, means for continuously removing the tubular bodies longitudinally one at a time from the other end of the reducing furnace, means in the oxidizing furnace for alternately blowing air longitudinally through opposite ends of the tubular bodies and means in the reducing furnace for alternately blowing a portion of the reducing atmosphere from said reducing furnace longitudinally through opposite ends of the tubular bodies therein;-

8. In apparatus for the-treatment oftubular metallic bodies prior to dipping in a coating bath, an oxidizing furnace having means for delivering into the furnace a heating and oxidizing atmosphere to surround the surfaces of the tubular bodies therein, a reducing furnace positioned laterally of one end of the oxidizing furnace and provided with means for delivering into the reducing furnace a reducing atmosphere to surround the bodies therein for continuously reducing the oxide coating of the tubular bodies to metal, means for continuously moving said tubular bodies broad-side in parallel orientation through the oxidizing furnace, means for continuously transferring said tubular bodies longitudinally one at a time from said one end of the oxidizing furnace to the adjacent end of the reducing furnace, means for continuously moving said tubular bodies broad-side in parallel orientation through the reducing furnace, means for continuously removing the tubular bodies longitudinally one at a time from the other end of the reducing furnace, means in the oxidizing furnace for blowing air longitudinally through the tubular bodies, means in the reducing furnace for blowing a portion of the reducing atmosphere from said furnace longitudinally through the tubular bodies therein, coating means positioned laterally of one end of the reducing furnace for coating the interior and exterior surfaces of the tubular bodies with a protective coating, means for continuously transferring the tubular bodies longitudinally one at a time from the reducing furnace to the coating means, and means for reversing the direction of delivery of said transferring means for continuously transferring the tubular bodies longitudinally one at a time from the reducing furnace in the opposite direction.

9. In apparatus for coating conduit sections and having a furnace for treating said conduit sections; the improvement comprising, spaced parallel screw conveyor-s in said furnace adapted to support opposite end portions of said conduit sections and convey the same through said furnace, and hold-down means comprising pivotally mounted arms disposed above opposite end portions of the conduit sections in said furnace for holding said sections on said conveyors including members carried by said arms for contacting said conduit sections near the end portions thereof, and means pivotally mounting said arms, to permit said arms and hold-down members to be swung from an operative position with the hold-down members in contact with the conduit sections near the end portions thereof to an inoperative position with the hold-downmembers clear of the conduit sections.

10. In apparatus for continuously coating conduit sections, a molten metal container comprising tank means for continuously dipping conduit sections beneath a body of molten metal for internally and externally coating the same, roller conveyor transfer means operatively associated with an entry side of the tank means for continuously introducing conduit sections laterally therein, guide means arranged in said tank means to guide said conduit sections substantially laterally downwardly in said tank means to a low point below the surface of said body of molten metal with one end of each conduit section maintained elevated with respect to the other end before reaching said low point in said tank means and then to guide said conduit sections substantially laterally upwardly toward the exit side of said tank means with reversed inclination of each of said conduit ends, conveyor means above said guide means and cooperable therewith for continuously moving conduit sections along the guide means below the surface of the molten metal, said conveyor means having elements to maintain the elevation of one end of each of said conduit sections with respect to the other end until said low point in the tank is reached and then to reverse the inclination of said section at said low point and maintain said reversed inclination thereafter, lift means adjacent the exit side of the tank for lifting conduit sections out of the body of molten metal, hold-down means adjacent lift means and cooperable therewith to maintain the inclination of each conduit section as said section is lifted from the molten metal, and means adjacent said lift means for removing said inclined conduit sections longitudinally from said tank means.

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